Low-vision users, and a lot of people over 50, need to increase the browser default font size to make text easier to read.
If your web content font sizes are set in absolute units, such as pixels, the user will not be able to re-size the text.
Relative units like EM and percentages “stretch” according to the screen size and/or user’s preferred font size, and work on a large range of devices.
Using relative units helps satisfy the WCAG 2.1 Guideline 1.4.4 Resize text Level AA.
Need to convert pixels to EMs?
Use this handy online tool, developed by Brian Cray: http://pxtoem.com
WEBSITE ACCESSIBILITY TESTING & REMEDIATION SERVICES: Mary Gillen is an experienced Website Accessibility Compliance Auditor and Remediator. She can test your website to determine if it meets accessibility standards:
WCAG 2.1: 312 checkpoints covering A, AA and AAA W3 accessibility guidelines
Section 508: 15 US federal guidelines covered by 59 accessibility checkpoints